[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH] virtio-balloon: fix QEMU 4.0 config size migrat
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH] virtio-balloon: fix QEMU 4.0 config size migration incompatibility |
Date: |
Wed, 10 Jul 2019 16:24:47 +0100 |
User-agent: |
Mutt/1.12.0 (2019-05-25) |
* Stefan Hajnoczi (address@hidden) wrote:
> The virtio-balloon config size changed in QEMU 4.0 even for existing
> machine types. Migration from QEMU 3.1 to 4.0 can fail in some
> circumstances with the following error:
>
> qemu-system-x86_64: get_pci_config_device: Bad config data: i=0x10 read: a1
> device: 1 cmask: ff wmask: c0 w1cmask:0
>
> This happens because the virtio-balloon config size affects the VIRTIO
> Legacy I/O Memory PCI BAR size.
>
> Introduce a qdev property called "qemu-4-0-config-size" and enable it
> only for the QEMU 4.0 machine types. This way <4.0 machine types use
> the old size, 4.0 uses the larger size, and >4.0 machine types use the
> appropriate size depending on enabled virtio-balloon features.
>
> Live migration to and from old QEMUs to QEMU 4.1 works again as long as
> a versioned machine type is specified (do not use just "pc"!).
>
> Originally-by: Wolfgang Bumiller <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
Reviewed-by: Dr. David Alan Gilbert <address@hidden>
Tested-by: Dr. David Alan Gilbert <address@hidden>
Tried 3.1->head and back
Tried head<->head (default options)
in both cases I tried ballooning the guest up and down
Dave
> ---
> include/hw/virtio/virtio-balloon.h | 2 ++
> hw/core/machine.c | 2 ++
> hw/virtio/virtio-balloon.c | 28 +++++++++++++++++++++++++---
> 3 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/include/hw/virtio/virtio-balloon.h
> b/include/hw/virtio/virtio-balloon.h
> index 1afafb12f6..5a99293a45 100644
> --- a/include/hw/virtio/virtio-balloon.h
> +++ b/include/hw/virtio/virtio-balloon.h
> @@ -71,6 +71,8 @@ typedef struct VirtIOBalloon {
> int64_t stats_poll_interval;
> uint32_t host_features;
> PartiallyBalloonedPage *pbp;
> +
> + bool qemu_4_0_config_size;
> } VirtIOBalloon;
>
> #endif
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 2be19ec0cd..c4ead16010 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -34,6 +34,7 @@ GlobalProperty hw_compat_4_0[] = {
> { "virtio-vga", "edid", "false" },
> { "virtio-gpu-pci", "edid", "false" },
> { "virtio-device", "use-started", "false" },
> + { "virtio-balloon-device", "qemu-4-0-config-size", "true" },
> };
> const size_t hw_compat_4_0_len = G_N_ELEMENTS(hw_compat_4_0);
>
> @@ -49,6 +50,7 @@ GlobalProperty hw_compat_3_1[] = {
> { "usb-tablet", "serial", "42" },
> { "virtio-blk-device", "discard", "false" },
> { "virtio-blk-device", "write-zeroes", "false" },
> + { "virtio-balloon-device", "qemu-4-0-config-size", "false" },
> };
> const size_t hw_compat_3_1_len = G_N_ELEMENTS(hw_compat_3_1);
>
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 11fad86d64..e85d1c0d5c 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -615,6 +615,22 @@
> virtio_balloon_free_page_report_notify(NotifierWithReturn *n, void *data)
> return 0;
> }
>
> +static size_t virtio_balloon_config_size(VirtIOBalloon *s)
> +{
> + uint64_t features = s->host_features;
> +
> + if (s->qemu_4_0_config_size) {
> + return sizeof(struct virtio_balloon_config);
> + }
> + if (virtio_has_feature(features, VIRTIO_BALLOON_F_PAGE_POISON)) {
> + return sizeof(struct virtio_balloon_config);
> + }
> + if (virtio_has_feature(features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> + return offsetof(struct virtio_balloon_config, poison_val);
> + }
> + return offsetof(struct virtio_balloon_config, free_page_report_cmd_id);
> +}
> +
> static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t
> *config_data)
> {
> VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
> @@ -635,7 +651,7 @@ static void virtio_balloon_get_config(VirtIODevice *vdev,
> uint8_t *config_data)
> }
>
> trace_virtio_balloon_get_config(config.num_pages, config.actual);
> - memcpy(config_data, &config, sizeof(struct virtio_balloon_config));
> + memcpy(config_data, &config, virtio_balloon_config_size(dev));
> }
>
> static int build_dimm_list(Object *obj, void *opaque)
> @@ -679,7 +695,7 @@ static void virtio_balloon_set_config(VirtIODevice *vdev,
> uint32_t oldactual = dev->actual;
> ram_addr_t vm_ram_size = get_current_ram_size();
>
> - memcpy(&config, config_data, sizeof(struct virtio_balloon_config));
> + memcpy(&config, config_data, virtio_balloon_config_size(dev));
> dev->actual = le32_to_cpu(config.actual);
> if (dev->actual != oldactual) {
> qapi_event_send_balloon_change(vm_ram_size -
> @@ -766,7 +782,7 @@ static void virtio_balloon_device_realize(DeviceState
> *dev, Error **errp)
> int ret;
>
> virtio_init(vdev, "virtio-balloon", VIRTIO_ID_BALLOON,
> - sizeof(struct virtio_balloon_config));
> + virtio_balloon_config_size(s));
>
> ret = qemu_add_balloon_handler(virtio_balloon_to_target,
> virtio_balloon_stat, s);
> @@ -897,6 +913,12 @@ static Property virtio_balloon_properties[] = {
> VIRTIO_BALLOON_F_DEFLATE_ON_OOM, false),
> DEFINE_PROP_BIT("free-page-hint", VirtIOBalloon, host_features,
> VIRTIO_BALLOON_F_FREE_PAGE_HINT, false),
> + /* QEMU 4.0 accidentally changed the config size even when free-page-hint
> + * is disabled, resulting in QEMU 3.1 migration incompatibility. This
> + * property retains this quirk for QEMU 4.1 machine types.
> + */
> + DEFINE_PROP_BOOL("qemu-4-0-config-size", VirtIOBalloon,
> + qemu_4_0_config_size, false),
> DEFINE_PROP_LINK("iothread", VirtIOBalloon, iothread, TYPE_IOTHREAD,
> IOThread *),
> DEFINE_PROP_END_OF_LIST(),
> --
> 2.21.0
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK